Method and device for closing a well in the ground

ABSTRACT

A method and device for closing a well with a casing in a formation in the ground are provided. The method has the steps of moving a cutting tool down into the well; removing a longitudinal portion of the casing by cutting the longitudinal portion into pipe wall pieces; removing the cutting tool; and setting a plug against the formation in the longitudinal portion from which the casing has been removed.

BACKGROUND OF THE INVENTION

This invention relates to a method of closing a well in the ground. More particularly, it relates to a method of closing a well in the ground wherein the well has a casing. The invention also includes a device for practicing the method.

When production from a ground well, particularly a petroleum well, has been discontinued, it is necessary to close the well in a way that protects against future outflow of well fluid and other substances from the well.

Above each pressure-bearing zone, it is common practice to place at least two independent barriers; including a suitable plugging material which is arranged to seal the well. In some cases, it is necessary to remove a section in the longitudinal direction of a casing in order for a barrier or a plug to be placed against the formation wall.

According to the prior art, the casing material is machined away by means of a hard-metal blade which is arranged on a pipe string. The pipe string is connected to a drilling vessel or an installation with the necessary drilling equipment. Chips from the machining must be transported up to the surface because the chips, which may be magnetic and may include relatively long chip coils, prevent tools from passing the portion if they are not removed.

Machining the longitudinal portion away from the casing by means of the prior art may take several days and is a very expensive operation.

SUMMARY OF THE INVENTION

One of the objectives of the invention is to remedy or reduce at least one of the drawbacks of the prior art.

The objective is achieved in accordance with the invention through the features which are specified in the description below and in the claims that follow.

A method is provided for closing a well with casing in a formation in the ground. The method has the steps of:

-   -   moving a cutting tool down into the well;     -   removing a longitudinal portion of the casing by cutting the         longitudinal portion into pipe wall pieces;     -   removing the cutting tool; and     -   setting a plug against the formation in the longitudinal portion         from which the casing has been removed.

The cutting tool may be a tool which is arranged to make cuts through the pipe wall as opposed to machining tools which are arranged to remove pipe material by chipping.

By cutting the longitudinal portion into pipe wall pieces, the production of voluminous chips is avoided. Alternatively, the pipe wall pieces that are produced are relatively easy to handle.

Further, the method may involve cutting the longitudinal portion by means of a fluid jet. By using a fluid jet, the further induction of magnetic forces into the pipe wall pieces is avoided and the pipe wall pieces may be allowed to fall down and remain in the well. If desired, the pipe wall pieces may be carried to the surface, for example, by means of a magnet.

The method may further have the steps of:

-   -   filling the lower portion of the well with filler;     -   cutting an inner casing at a lower position in the well than the         position at which the longitudinal portion is located; and     -   removing the upper portion of the inner casing.

The method may further have the step of connecting the cutting tool to the surface by means of coiled tubing. The method thereby makes it possible for the well to be shut down without the use of a drilling rig.

The method can be practiced by means of a cutting tool for cutting the longitudinal portion of a casing. The cutting tool may have a nozzle head rotatable around its longitudinal axis. The nozzle head has at least one nozzle and is connected to coiled tubing. The coiled tubing may extend to the surface, and the cutting tool is connected to the casing by means of an anchor.

The anchor may be a fixed anchor or a rolling anchor, and the cutting tool may be provided with an actuator for moving the nozzle head axially.

In an embodiment in which the anchor is fixed, the actuator may be used for axial movement of the nozzle head during the cutting operation. If a rolling anchor is used, the coiled tubing can be moved axially in the well without the use of a separate actuator.

In a further embodiment, the cutting head may be provided with a pendulum nozzle. The pendulum nozzle, which is of a design known in the art, is arranged to pivot the fluid jet while the nozzle head is kept stationary.

The cutting tool may be provided with a change-over valve which is arranged to selectively direct a fluid flow to a desired nozzle. For example, the fluid flow may be directed to a cutting nozzle during the cutting operation and then directed to a cleaning nozzle during a subsequent cleaning operation.

The method and device according to the invention enable a considerable reduction in the time spent on closing petroleum wells while, at the same time, using considerably simpler equipment compared with the prior art. The invention thereby provides for a substantial reduction in costs connected with closing and finishing off wells.

BRIEF DESCRIPTION OF THE DRAWINGS

The following is a description of an example of a preferred embodiment which is visualized in the accompanying drawings, in which:

FIG. 1 shows schematically a well which has been prepared for a cutting operation according to the invention.

FIG. 2 shows schematically a section, on a larger scale, of a cutting head.

FIG. 3 shows a cutting pattern in the wall of the casing.

FIG. 4 shows schematically, on a smaller scale, a well after a plug has been set.

DETAILED DESCRIPTION OF THE INVENTION

In the drawings, the reference numeral 1 indicates a petroleum well in a formation 2. An inner casing 4, a second inner casing 6 and other casings 8 are cemented into a borehole 10 by means of a cementation mass 12.

A seal 14 is created between the inner casing 4 and the second inner casing 6.

In FIG. 1, the well 1 is shown after preparatory work has been carried out. The preparatory work may involve filling the lower portion of the inner casing 4 with filler 16, cutting the inner casing 4, and removing the upper portion (not shown) of the inner casing 4 from the well 1.

Coiled tubing 18 with a cutting tool 20 fitted thereon is shown in the well 1. The cutting tool 20 may be positioned and held fixed inside the second inner casing 6 by means of an anchor 22.

The cutting tool 20 includes a tool housing 24 with necessary components known in the art, not shown, for controlling the cutting operation. An actuator 26 is arranged to move a rotatable nozzle head 28 in the longitudinal direction of the well 1.

In this preferred embodiment, the nozzle head 28 includes a change-over valve 30 for selectively directing pressure fluid, which is supplied via an actuator channel 32, from the coiled tubing 18 to a cutting nozzle 34 or a cleaning nozzle 36, as shown in FIG. 2.

The change-over valve 30 may be a so-called sequence valve which changes its position every time the fluid pressure is relieved.

When the cutting tool 20 is positioned in the well 1, the cutting may be initiated by fluid containing abrasive material flowing to the cutting nozzle 34 at a relatively high pressure via the coiled tubing 18 and the change-over valve 30.

The nozzle head 28 moves the cutting nozzle 34 along a predetermined path forming, for example, the cutting path 38 in the pipe wall 40 of the second inner casing 6 as it is shown in FIG. 3.

By subsequently cutting along the paths 42, pipe wall pieces 44 are formed from the longitudinal portion 46 of the second inner casing 6.

By switching the change-over valve 30, pressure fluid is carried to the cleaning nozzle 36, resulting in the pipe wall pieces 44 being washed down or into the well 1.

The part of the cementation mass 12 that may be behind the longitudinal portion 46 of the second inner casing 6 is also removed by means of fluid jets from the nozzles 34, 36 of the nozzle head 28.

After the well 1 has been prepared, the coiled tubing 18 and the cutting tool 20 are pulled from the well 1, after which a plug 48 is set against the formation 2 in the longitudinal portion 46 in a manner known in the art, as shown in FIG. 4. In the present embodiment, a rubber type plug 48 is shown. A person skilled in the art will understand that any suitable plug may be used.

In an alternative method, not shown, the longitudinal portion 46 may be chosen to be a location at which two or more casings 6, 8, one outside another, will have to be cut away to expose the formation 2.

Although exemplary systems, methods, and structures are described in language specific to structural features and/or methodological acts, the subject matter defined in the appended claims is not necessarily limited to the specific features or acts described. Rather, the specific features and acts are disclosed as exemplary forms of implementing the claimed systems, methods, and structures. 

1. A method of closing a well with a casing in a formation in the ground, the method comprising the steps of: moving a cutting tool down into the well; removing a longitudinal portion of the casing; setting a plug against the formation in the longitudinal portion from which the casing has been removed; and cutting the longitudinal portion of the casing into pipe wall pieces.
 2. The method of claim 1 further comprising the step of: cutting the longitudinal portion is carried out by a fluid jet.
 3. The method of claim 1 wherein the pipe wall pieces remain in the well.
 4. The method of claim 1 comprising the steps of: filling a lower portion of the well with filler; cutting an inner casing at a lower position in the well than the longitudinal portion; and removing an upper portion of the inner casing.
 5. The method of claim 1 further comprising the step of: connecting the cutting tool to the surface by a coiled tubing.
 6. A cutting tool for cutting a well casing, the cutting tool comprising: a nozzle head with at least one nozzle rotatable around a longitudinal axis wherein the nozzle head is connected to a coiled tubing that extends to the surface and further wherein the cutting tool is connected to the casing by an anchor.
 7. The cutting tool of claim 6 wherein the anchor is a rolling anchor.
 8. The cutting tool of claim 6 further comprising: an actuator for moving the nozzle head axially.
 9. The cutting tool of claim 6 wherein the nozzle head has a pendulum nozzle.
 10. The cutting tool of claim 6 further comprising: a change-over valve which is arranged to selectively connect a fluid flow to a desired nozzle. 